Overweight and obesity in childhood have tripled since 1980 and currently stand at 30% and 17% among 2-19-year-olds (Ogden et al., 2010), respectively. Excess fat mass in childhood is a strong predictor of obesity in adulthood and can lead to life-threatening medical conditions, such as diabetes, coronary heart disease, and certain cancers (Flegal et al., 2010). Previous studies have utilized BMI as the primary outcome and failed to measure diet and activity-related effects on actual fat mass. Abdominal adipose tissue (central adiposity) in children has been previously correlated with higher plasma lipids, elevated blood pressure, and insulin resistance (Daniels et al., 1999; Morrison et al., 1999; Krekoukia, 2007). Furthermore, children above the recommended values for waist circumference-for-age (≥75th percentile) and waist-to-height ratio (≥0.5) have elevated lipid profiles and higher insulin resistance (Savva, 2000). These studies suggest that central adiposity may be the most clinically relevant distribution of body fat in children, as is the case with adults. The overall objective of this research was to determine how media use and diet intake, independently or in concert, affect central adiposity in prepubertal children. Our central hypothesis was that poor diet quality is related to increased central adiposity, independent of aerobic fitness. The aims of our study were to determine the relationships between: 1) media use and central adiposity; and 2) diet and central adiposity.
Prepubertal children (113 females and 116 males) were recruited from an on-going NIH-funded afterschool physical activity research trial (FITKids). Pubertal staging was assessed using a modified Tanner Staging System (Tanner, 1962; Taylor, 2001). Parents reported their child’s weekday and weekend television (TV) and videogame use. Maximal oxygen consumption (VO2max) and one 24-hour recall were used to assess fitness level and dietary intake, respectively. Dual energy X-ray absorptiometry (DXA) was used to measure whole body percent fat mass (WB %FM) and central adiposity (FM-abd). Gender-specific waist circumference-for-age percentiles (WC-age) and waist-to-height ratio (WHtR) were determined to further assess central adiposity.
Body composition results showed that females (N=105) had significantly higher WB %FM (p<0.001) and FM-abd (p<0.001) compared to males (N=109). Among females, pubertal staging was positively related to WB %FM (r=.37, p<0.001) and FM-abd (r=.48, p<0.001). Pubertal staging was not related to adiposity measures among males (p>0.05). However, fitness was inversely related to FM-abd among females (r=-.59, p<0.001) and males (r=-.47, p<0.001).
Weekend TV time among females was related to increased FM-abd (r=.17, p=0.03) and WHtR (r=.22, p<0.001), after controlling for fitness. Females who watched more than 2 hours of TV/day had significantly higher FM-abd (p=0.03). Females above the recommended WC-age cutoff (≥75th percentile) had significantly higher cholesterol-saturated fatty index (CSI) (p=0.04) and intake of added sugars (p<0.001). CSI was the only dietary variable related to increased FM-abd among females, after controlling for both fitness and energy intake (r=.26, p=0.03). However, no diet-body composition relationships remained significant after controlling for fitness and energy intake among males.
Standard linear regression models suggested that the strongest predictors of FM-abd among females were pubertal staging (β=.418, p<0.001) and fitness (β=-.405, p<0.001). The addition of energy intake, added sugars, and CSI accounted for an additional 10% of the variance in FM-abd. The same model explained 53% of the variance in WHtR. Among males, age was a positive predictor (β=.306, p=0.005) and fitness was a negative predictor (β=-.453, p<0.001) of FM-abd. Subsequent addition of diet variables only accounted for 0.5% of the variability in FM-abd. Fitness was the strongest predictor of WHtR (β=.331, p=0.005). Among females, pubertal staging accounted for 13% of the variability in WB %FM. Energy from protein was a positive predictor of whole body adiposity (β=.265, p=.007). However, the contribution of energy from protein became non-significant when energy from fat was included in the model. The overall model accounted for 52% of the variability in WB %FM. Among males, age (β=.335, p=.001) and fitness (β=-.427, p<0.001) remained the strongest predictors of WB %FM.
In conclusion, females and males differed across all measures of adiposity, including the primary outcome of FM-abd. Weekend TV time appeared to influence energy intake, cholesterol and added sugars, however, these relationships attenuated once energy intake was controlled for. Added sugars and cholesterol-saturated fatty acid index were important predictors of central adiposity. After controlling for fitness and energy intake, the influence of these nutrients was non-significant among males. Collectively, these results suggest that dietary and sedentary behaviors may have differential health-related outcomes for prepubertal children based on gender. Body composition appeared to be significantly influenced by pubertal staging in girls and chronological age in boys. Therefore, our findings have implications for nutrition intervention efforts targeting obesity prevention during the critical period of preadolescence. Future work is needed to assess influence of diet and media on central adiposity as children transition into adolescence.